This invention relates to a bleach-fixing solution and a method for processing a light-sensitive silver halide color photographic material by using the same. More particularly, this invention pertains to a method for processing of a light-sensitive silver halide color photographic material which has been dramatically improved in storage stability of a bleach-fixing solution employed and also improved in bleaching speed.
In the prior art, as the so called bleaching agent for removing the image silver in a light-sensitive silver halide photographic material, oxidizing agents such as red prussiate, dichromate, persulfate, iron chloride, etc. have been employed, but they involved problems in toxicity or corrosion of the members in processing machines and are not sufficiently satisfactory in practical application.
In recent years, in view of absence of problems with respect to toxicity, methods have been practiced, in which an aminopolycarboxylic acid metal complex is utilized as the oxidizing agent in a bleaching solution or a bleach-fixing solution.
However, an aminocarboxylilc acid metal complex has a weak oxidizing power and therefore has the drawback of slow bleaching speed, which brings about the drawback that no one-bath bleach-fixing processing, particularly required for rapid processing of a high sensitivity light-sensitive silver halide color photographic material, is possible. Practically, ethylenediaminetetraacetic acid iron (III) complex salt, which is considered to have a potent bleaching power among the aminopolycarboxylic acid metal complexes, is utilized also as the bleach-fixing solution in some applications. However, it is deficient in bleaching action in high sensitivity light-sensitive silver halide color photographic materials composed primarily of silver bromide or silver iodobromide emulsions, particularly color paper for photographing, color negative film for photographic and color reversal film containing silver iodide, whereby traces of image silver will remain even after prolonged processing to give poor silver elimination characteristic. Further, as the increase of silver salt or iodine ion concentration dissolved and accumulated in the processing solution, bleaching power will be markedly lowered. Particularly, at a pH 4 or higher, this will appear markedly with a dissolved accumulation of 5 g of silver ions per liter. On the other hand, at a pH value less than 4, silver ion accumulation has only very small effect on the bleaching power. Moreover, in a bleach-fixing solution in which an oxidizing agent together with a thiosulfate and a sulfite are co-present, due to lowering in redox potential, poor silver elimination tendency will markedly be exhibited.
In the prior art, for overcoming these problems, a bleaching promotor is added to a bleach-fixing solution using primarily ethylenediaminetetraacetic acid iron (III) complex salt as the oxidizing agent, as disclosed in Japanese Patent Publication Nos. 8506/1970, 556/1981 and Japanese Unexamined Patent Publications Nos. 280/1971 and 5630/1974. However, no satisfactory bleaching promoting effect can be necessarily obtained or there is involved the problem such that the silver accumulated by dissolution will form a slightly soluble precipitate. Thus, none of these solutions of the prior art proved to be acceptable as the practical bleach-fixing solution for high sensitivity silver halide color photographic materials.
As an alternative method, it has also been practiced to perform processing, when employing an ethylenediaminetetraacetic acid iron (III) complex salt at a low pH region so that its bleaching power may strongly be exhibited. This method, however, is well known to have serious problems such that the co-existing thiosulfate or sulfite is readily decomposable to give low stability of the solution, and also that the chromogenic dye, particularly a cyan dye is liable to be converted to leuco form, thereby to give no sufficient sensible image.
If processing is conducted at a higher pH side for solving this problem, while the leuco dye may be decreased, silver elimination characteristic will be lowered as the increase of pH, simultaneously with disadvantageous formation of dye staining through coupling between the oxidized product and the residual coupler (hereinafter called as stain), whereby no satisfactory bleach-fixing processing performance could be obtained.
As another method for solving the problems, one may easily think of a method in which a coupler which may hardly form a leuco dye, particularly a cyan coupler of the phenol type having 2,5-diacylamino group, is employed and processing is performed with a bleach-fixing solution using a low pH ethylenediaminetetraacetic acid iron (III) complex salt as the oxidizing agent or a bleach-fixing solution using a glycoletherdiaminetetraacetic acid iron (III) complex salt as the oxidizing agent. However, even if leuco formation of cyan dye or bleaching speed may be attained as expected, decomposition of co-existing sulfite or thiosulfate will occur noticeably in a low pH bleach-fixing solution. Therefore, such a method can hardly be practically applicable with respect to stability of the processing solution.
Thus, in the case when a high sensitive light-sensitive color photographic material for photographing is processed with the use of a bleach-fixing solution containing an ethylenediaminetetraacetic acid iron (III) complex salt of the prior art, there can be seen no sufficiently satisfactory approach, in which the four problems of rapid silver bleaching power, leuco formation of cyan dye, prevention of generation of stain and further storage stability of bleach-fixing solution (particularly sulfide formation from thiosulfate) are simultaneously solved. Accordingly, appearance of a bleach-fixing processing system for a high sensitivity light-sensitive color photographic material, which can solve these four problems at the same time as required for bleach-fixing solution, has been earnestly sought after.